Transmission by modulated waves



Nov. 6, 1928. 1,690,227

R. A. HESNG A TRANSMISSION BY MODULATED WAVES Filed Feb. 28, 1925 2 Sheets-Sheet l 0R 55000 -Amaaafv 4, 2M 60am/ P f ONNHOOON loo 0am/ Nov. 6, 1928.

R. A. HEISING TRANSMISSION BY MODULATED WAVES Filed Feb. 28, 1923 2 Sheets-Sheet QQQNIQQN NNN @Q GOSH? DQNN "III- gwfua'nffoz A. Hesinlg Patented Nov. 6, 1928.

UNITED STATESI PATENT OFFICE.

RAYMOND A. HEISING, OF MILLBURN, NEW JERSEY, ASSIGNOR TO WESTERN ELEC- TRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

TRANSMISSION BY MODULATED WAVES.

Application led February 28, 1923. Serial No. 621,710.

This invention relates broadly to signaling and'ii'iore particularly to multiplex telA epbony conducted either by line wire or radio.

One of the objectsof the invention is to enable simultaneous transmission of a plurality of signals or control waves on a common carrier wave without interference or cross modulation.

A further object of the invention is to provide for multiplex telephone transmission by means of a. single carrier wave modulated by a plurality of signal waves of different frequency ranges without cross-modulation between the vaiious signal waves. i

Another object of the invention is to provide for multiplex telephone transmission by means of a single carrier wave generator and a number of separate signaling channels without transmission of the carrier Wa-ve frequency to the receiving station.

Another obje-ct is to provide for modulation of carrier waves by signal waves or side bands representating signals to produce new signal-representing side bands and for the suppression of both the carrier Waves and the signal waves or side bands used for modulation from the output current.

Another object of the invention is to provide a receiving circuit cooperating with the multiplex transmitting system of this invention wherebythe carrier wave frequency is re.- stored at the receiver and the difiere-nt signals are separated.

A further object of the invention is to provide a circuit arrangement at a transmitter for connecting any number of separate signaling circuits to the modulator circuit whereby separate signaling channels are developed, effectively spaced in frequency by predetermined fixed Jfrequencies supplied independently to each or each but one of the signaling channels.

A still further object is to provide for the elimination of cross modulation between the side frequencies in the several channels of the transmitter circuit by limiting the waves transmitted to either the upper or lower side bands of the single carrier wave.

Another object of the invention is to pro vide mea-ns at the receiver for passing the side frequencies received to selector circuits, isolating the several signaling frequencies, and rceiving the signals on different channels independently one from the other.

Other and further objects of the invention will be understood from the following specilication and accompanying drawings in which:

Fig. -1 is a circuit diagram showing the arrangement of transmitting apparatus of a multiplex telephone system and Fig. 2 is a circuit diagram Qf the receiving circuit einployed.

The invention relates both to the system and method of operati on of the multiplex telephone arrangement herein described.

The transmitting system shown in Fie. 1 includes a generato-r 1-of carrier wave requency which may be valued for purposes of illustration at 100,000 cycles, rep-resented as frequency C. A balanced electron tube modulator 2 is used consisting of two electron tubes 3 and 4 oppositely related to the carrier source with reference to grid excitation, that is, the carrier wave is applied to the two tubes in opposite phase. The carrier wave energy is impressed on the moulator by transformer 5 having primary winding 6 and secondary windings 7 and 8. The modulator circuit includes grid battery 9, a battery A for exciting the filament circuits of tubes 3 and 4 and source B for energizing the plateV circuits. The oiitp-ut circuit of the modulator tubes includes primary windings 10 and 11 of transformer 12 having secondary winding 14.

rlhe output current of the balanced modu lator includes the desired side frequency waves and an unmodulated carrier wave coinponciit. 'lhis unmodulated carrier wave component may be neutralized by an equaly amplitude and opposite phase wave of the carrier frequency applied through an amplfier 15 shunting the modulatin g system in the manner illustrated in England Patent No. 1,258,548 dated March 5, 1918, reissued April 19, 1921 as N0. 15,089.

The input circuit of amplifier 15 is connected through an autotraiisformer 16 to the terminals of the generator 1, the purpose of the autotransformer connection being to regulate the voltage impressed upon the input circuit of the amplifier 15. The output circuit of the amplifie-r is connected to a phase regulator 17 of suitable form and the voltage across a scot-ion ofthe network is then applied to the input circuit of power ampliers 20. This volt-age has the same. frequency as that produced at the terminals of carrier Wave generator 1 but it is so regulated as to intensity and phase as to exactly neutralize the unmodulate carrier wave component of the output current of the modulator.

1n the input circuit of the modulating tubes means are provided, such as" transformers 21, 22 and 23, for inductively connecting any number of different voice si naling circuits with the modulator. T e windings 2l, 22 and 23a are connected in the input circuit of the modulator while windin s 2l", 22b and 23b are connected to each o the signaling circuits respectively. Each of the signaling circuits consists of a microphone 25, transformer 26 and battery 27 related to the input circuit of an electron tube device 28. rlhe device 28 in the first channel serves merely as an amplih'cr and may be omitted from this channel if amplification of the s eech waves is unnecessary. Such a channel or example is that containing the filter F1 which passes speech frcquenc currents of from 200-2000 cycles per secon The output from this band filter is then impressed on the grid circuit of the balanced carrier wave modulator as the signal of one channel of the system. A signal apllied in this manner ma be considered to e applied to the two tu es in the same phase.

In the other channels the device 281 functions as a modulator and its input circuit is supplied with continuous waves by a source 50 of oscillations which in one channel may be, for example of 2,000 cycles frequency. The voice rcquencies are superimposed in the grid circuit together with the current of 2,000 cycle frequency delivered by the generator. The output of the electron tube 28a, which operates as a mod ulator, furnishes to a band filter F2 one side frequency band which ranges between 2,200 cycles and 4000 cycles. Filter F2 is designed to transmit currents within this range to the exclusion of other currents impressed upon it. The band filters employed in the circuits of the present application are of the Campbell tipe shown in Patents Nos. 1,227,113 an 1,227,114 anted May 2,2, 1917 to George A. Campbel. The output from this band filter is then transferred to the grid circuit of the balanced carrier wave modulator 2 and transmitted as a second signaling channel. It will be noted that the wave filter F2, transmits a band of waves representing speech but with'all frequencies increased by 2000 cycles.

Similarly another speech signal increased in frequency by energy supplied from a generator of 4000 cycles developing a side frequency between 4200 and 6000 cycles is also supplied to the grids of the balanced carrier wave modulator 2. This signaling circuit includes a band filter F8 which eliminates all frequencies except those side frequencies between 4200 and 6000 cycles. The filters F1, F2, and Fa thus supply speech bands of normal width but ranging one above the other. These are impressed upon the modulatino' circuit 2. Another signaling channel may llie developed by effectively increasing the speech frequency band by a (i000 cycle frequency giving a side frequency ranging between limits of 6200 and 8000 cycles and so on. Any number of such circuits can be employed wherein the modulations caused by the speech frequencies are superimposed upon local generating circuits of such frequencies as 2000, 4000 and 0000 cycles or more. The precise increase in frequency of any of the signal waves is immaterial so long as the resultin bands impressed on the grid circuit of te balanced modulator 2 do not overla in frequency. Preferably these resulting ands will be separated by a certain frequency interval to permit goed selectivity at the receiving station without recourse to elaborate selecting means.

Having modulated the carrier wave from source 1 at the various modulation frequencies a typical one of which might be represented by S, the output of the tubes ot' the circuit 2 is then transferred through the split primary winding 10 and 11 to the grid cir cuit 14 of the power amplifier tubes 20. The phase adjuster 17 and the inductance 10 are adjusted so that an unmodulated carrier fre quency component is supplied to the grid circuit 14 which will just neutralize the unmodulated carrier frequency component supplied from'the moderator' circuit 2 as a rcsult of its repeating action. 'l`he output ot the power amplifier tubes is then delivered to a band filter F'l which preferably is capable of passing frequencies represented as C-S or G+S but which may transmit both G+S and C" S, the frequency S representing any frequency of a current impressed from any signal channel upon the input cir cuit of the balanced modulator 2. Accordingly in the particular arrangement illustrated G+S typifics a band of frequencies ranging from 100,200 to 100,000 cycles. Since the carrier frequency C is eliminated there is no component of carrier frequency transmitted. The band filter may therefore be capable of passing frequencies (C--S) between 94,000 cycles and 99,800 cycles or (G+S and Cr-S) 94,000 to 100,000 cycles. The output of this band filter is then delivered to an antenna radiating system 80 or to a line wire system.

The received wave from such a system will contain frequencies covering the entire range transmitted. It is desirable to introduce energy of the original carrier wave frequency by supplying a local source of oscillations which is identical in frequency with the ori ginal carrier wave frequency. In Fig. 2 is shown the receiving system wherein energy llo is brought into the station by the antenna system 33 or the line wire system. The am- )litude of the initial received ener may be increased by any desired number o stages of radio frequency amplification represented by electron tube 36. A wave of carrier frequency is introduced by a suitable generator 35. The amplified received energy and the locally supplied energy of carrier frequency are impressed on the grid circuit of a detector tube 37. The detecting action of this tube 37 is such as to produce in the output circuit of this tube currents whigch contain frequency components between 200 cycles and 6,000 cycles, corresponding to the modulating frequencies supplied to the balanced modulator 2 at the transmitter. The output of the detector circuit is delivered to a band filter FR which filter suppresses any current of the carrier wave frequency that may be inthe plate circuit of the detector tube and allows only frequencies between 200 and 6,000 cycles to pass on to the amplifier 39 which is common to all the signaling channels. The output of the amplifier 39 is connected to a number of circuits corresponding to the number of signaling channels at the transmitter. By way of illustration three separate circuits are shown connected to the secondary of the audio frequency transformer 40. In circuit 41 a band filter FE1 is connected which allows frequencies varying between 200 to 2000 cycles to pass. These currents are of audible frequency, and represent speech. They may be am lified in a vacuum tube amplifier circuit 41 efore being impressed upon the receivers 48 to reproduce the speech corresponding to the channel containing the filter F1 at the transmitting station.

In the second circuit 42 a band filter 'FRZ allows currents of frequencies between 2200 and 4000 to pass. The currents of this band of frequencies are then passed on to a detector tube 46 which isprovided with a local source of oscillations 45. The local source of oscillations in this case is a 2000 cycle generator. The difference in frequency between the incoming signal waves passed by filter FB2 and the 2000 cycle oscillator will give rise to a signal in the telephones 48 which will be equal to voice frequency` or, in other words, from 200 to 2000 cycles. A filter FAZ is used in this circuit between the output of the amplifier tube and the telephone receivers. This filter may be o-f the band or low pass filter type, preferably of the low pass filter type, wherein frequencies below 2000 cycles are permitted to pass to the telephone receivers while excluding the low frequency note of the local oscillator 45.

In circuit 43 a band filter FR3 which is capable of passing frequencies between 4200 and 6000 cycles is connected. The output of this band filter FR3 is delivered to the grid of a detector tube 47, the input circuit of from200 to 2000 cycles is effectively increased in all but one of the channelsby predetermined fixed frequencies determining the si nalincr channels cach of which independent y modu ate a single carrier wave without cross modulation and with the carrier frequency eliminated. A

A characteristic feature of theinvention is in the application of signal or modulating waves to the modulator circuit 2 in such a manner that the signal waves themselves are suppressed in the modulator as distinguished from the method in which the signal Waves are so applied as to be repeated to the output circuit and the carrier wave so applied as to be suppressed. Since the modulator itself does not sup press the carrier wave in the present arrangement the channel 16, 15 and 17 is provided for this purpose.

At the receiving station, a local source of oscillations of the principal carrier frequency may be used to produce in the output circuit of the first detector, waves corresponding in frequency to the separate signals applied to the modulator input. These separate signals are selected by band filters and each of these but one is beaten with locally produced low frequency oscillations of 2000, 4000 cycles, etc., in a second detector, the output circuit of which is provided with a low pass filter which will eliminate the low frequency beating oscillations and transmit tbe original speech signals. V

One of the separate signals is of speech frequency and is applied directly to the receiving telephone or low frequency line without the intervention of a local source of os-l cillations.

In the present specification a band of frequencies of from 200 to 2000 cycles per second is chosen as illustrative of a bandsuitable for commercial practice. lWider or narrower bands and higher or lower frequency ranges may be used.

The band filter FT may be relied upon to suppress any component of unmodulated carrier frequency not suppressed by the channel 15, 16,17. If it is too difiicult or expensive to construct a filter to suppress 100,000 cycles and pass 100,200 cycles the speech frequency channel containing the filter F1 may be omitted.

While I have illustrated the invention in a particular embodiment, such as employing a circuit for suppressing the carrier wave frequency at the transmitter, it should be understood that modications may be made, such as eliminatin the restoring carrier frequency at the receiver and allowing the carrier frequency to be transmitted, without departing from the spirit of my invention as covered by the appended claims.

What is claimed is: l

1. In a signaling system tWo modulator devices for modulating a carrier Wave in accordance with a plurality of separate signaling waves, means for impressing in the saine phase the plu ality of separate signaling waves on the modulators, means for impressing the carrier wave upon the modulating devices in opposite phase whereby all of the signals are transniitted with a minimum of cross modulation, and additional means for neutralizing the unmodulated component of the carrier wave frequency in the output circuit of said devices.

2. In a signaling system a source of carrier wave energy, a modulator consisting of a pair of oppositely connected electron tubes, a plurality of signaling circuits connected to said tubes to apply voltages thereto in the same phase', and means for suppressing the unmodulated component of carrier wave frequeney.

B. In a signaling system a modulator circuit, means for impressing carrier waves and signaling waves on said modulator circuit, means for suppressing the unmodulated carrier frequency component from the output circuit of said modulator, and means for supilying signaling waves to said modulator in such a way that currents of the signaling wave frequency do not appear in the output circuit.

4. A system comprising two space discharge devices having input circuits and output circuits, a plu ality of sources of Waves each involving a variety of frequencies in a variety of phase relations connected to said input circuits to apply electromotive forces thereto in the same phase relation, a source of waves essentially of a sin le fre ueney connected to similar circuits olf said evices to apply electromotive forces thereto in opposite phase relation, an output channel for conducting waves from said devices, and a channel from said last named source of waves connected to said output channel including phase and amplitude controlling means.

A modulating system comprising a plurality of sources of signaling Waves each representing a signal or message, a space discharge device modulator comprising two devices each having a grid-cathode circuit, connections between said sources and said grid cathode circuits, each said connection being similar to the others, and the otentials impressed on the respective gri s from said connections each bein equal to the others and having the same p ase, a carrier source and means for impressing waves from said rarrier source on said grid-cathode circuits in relatively opposite phase.

In a plural channel tele hone system, a plurality of sources of speecii representing waves, means for translating the frequencies of the waves from each but one of said sources to a high frequency range so that, the translated and untranslated speech representing waves are arranged in frequency one above the other, means for modulating a carrier" wave in accordance with the resultant speech representing waves and suppressing hoth the carrier and speech representing waves to produce corresponding speech representing waves of translated frequency range, and a receiving system comprising means for isolating and observing at least one of the speech representing waves independently of theiothers.

In witness whereof, I hereunto subscribe my name this 27th day of February, A. D. 1923.

RAYMOND A. HEISING. 

